A knife represents a hand-held cutting tool with a cutting edge or blade. It may also have a handle. Originally made from rock, bone, flint, or obsidian, knife blades today are typically fashioned from iron, steel, ceramics, or titanium.
While knives may be used as a weapon, they are more commonly employed by people as useful tools in food preparation, dining, meat processing, hunting, construction, work projects, and hobbies for cutting or slicing an object. Many different types and designs of knives are known, but most of them share the trait of one or two sharpened blade edges.
But, over time, these sharpened edges of the knife blade will become dull or damaged. Blades are damaged due to compressive force arising from the user pressing the knife blade cutting edge into a hard object like bone, ice, a hard cutting board, or other hard object, or simply by repetitive use. The knife blade may also become bent from sideways pressure applied against the blade. Both of these forces tend to roll the knife blade's cutting edge due to the ductile characteristic of the metal material used in the blade. Moreover, tougher or abrasive materials will cause the blade to become dull more quickly.
Dull blades do not cut as easily or precisely, and can create a danger to the end user by requiring greater hand force to make a cut. Moreover, dulled blades can include burrs or ragged edges with regions along the cutting surface that are out of alignment with each other. Such misaligned blades can damage the material being cut, or produce an inferior cut by tearing or sawing the material being cut as opposed to a smooth, clean cut.
Therefore, such dulled knife blades must be periodically sharpened. This is typically a process in which the knife blade is manually ground against a hard, rough surface like a stone, or a soft surface containing hard particles. Metal can be removed from the knife blade in order to form a new edge along the blade. Typically, a grinding wheel or a whetstone is used. These sharpening stones come in varying grit degrees from very coarse to very fine, and can be described as hard or soft depending upon whether the grit comes free of the stone during the grinding operation. Ceramic hones are also commonly used, especially when fine grit size is desired. Coated hones with an abrasive diamond-based surface provide yet another option. Mineral oil often is used during the grinding application to separate the loosened grinding particles from the knife blade edge to prevent damage to the blade.
However, grinding constitutes a precise manual operation in which the angle of the cutting edge of the blade must match the angle of the whetstone or grinding wheel surface. The smaller the angle between the blade and stone, the sharper the knife will be, but at the same time, less side force is required to damage the knife blade by bending the cutting edge over or even chipping it off. The edge angle represents the angle between the blade and the stone. For symmetrical double-ground, wedge-shaped knife blades, the angle from one edge to the other edge of the blade will be twice the edge angle.
The cutting edges of the knife blade may also be straightened by a hand-held sharpening steel. The sharpening steel constitutes a hardened cylindrical, triangular or other shaped rod having a small diameter. This sharpening steel may have a smooth, polished exterior surface, or may be somewhat abrasive. It may also feature slight ridges or ribs running along the length of the rod. A butcher steel constitutes a round file with teeth running the long way, although it may also be smooth. As the knife blade with its cutting edge is swiped along the sharpening steel, the steel will exert high localized pressure against the cutting edge to straighten the turned edges of the cutting edge back into proper alignment. Unlike grinding, such steeling process does not usually remove metal from the blade edge.
Knives used by barbers are often manually stropped after steeling in order to polish the sharpened cutting edge. This is often done with a leather strap impregnated with an abrasive compound like chromium (III) oxide particles. This operation does not remove any metal material from the blade edge, but produces a very sharp edge.
While steeling represents a less aggressive form of sharpening than grinding, it still is important to swipe the knife's blade at a proper angle with respect to the sharpening steel. Moreover, the two cutting edges of the knife must be swiped the same number of times against the steel or else the cutting edge will be pushed again out of alignment. U.S. Pat. No. 3,942,394 issued to Juranitch in 1976 for a hand-held finishing sharpener includes fold-out wings that act like sharpening steels accompanied by a handle that provides a visual guide for maintaining the proper angle of the knife's cutting edge along the wings. This may make it slightly easier for the user to estimate the proper angle for the knife blade sharpening operation.
A manually-operated knife sharpening device referred to as a MOUSETRAP STEEL sharpener that is further disclosed in U.S. Pat. Nos. 4,934,110 and 5,655,959 issued to Juranitch provides another example. It constitutes a bench-top mounted, vertical base member having a vertical slot partially bisecting the base member from its top edge. Pivotably mounted to the base member are two counterweights having equal masses. A pair of upwardly curved sharpening steels is connected to the upper and inner ends of the counterweights and extend toward each other in a crossed relationship, intersecting at and along the slot. As a knife blade is pushed down through the slot, it engages the sharpening steels at this intersection point and pushes the steels inwardly, sharpening the opposing cutting edges of the knife blade simultaneously as the knife blade is swiped along the sharpening steels. A pivotably-mounted wiper wing under the influence of its own counterweight polishes the sharpened blade. A pair of cams that are eccentrically mounted to the base member act to arrest the lateral movement of the steels during the knife sharpening operation, as well as to define the downward resting point of the counterweights when the sharpening steels are in their standby position when the knife blade is disengaged. See also U.S. Pat. No. 9,545,703 issued to Juranitch et al. and U.S. Ser. No. 15/610,169.
However, these cams must be carefully adjusted in their eccentric positions along the base member prior to the knife sharpening operation to define how high or low the crossed intersection point of the steels will be situated over the slot. A higher position requires greater force applied to the knife blade during the sharpening operation resulting in this higher intersection point of the steels producing a less-sharp cutting angle along the knife blade. A lower intersection position on the other hand requires less force applied to the knife blade during the sharpening operation resulting in a sharper cutting angle produced by the steels along the knife blade. Thus, the MOUSETRAP STEEL sharpener requires the user to know in advance the angle of the cutting edges that must be produced along the sharpened knife blade, and to precisely adjust in advance the cams' positions to achieve this desired angle. This requires skill and patience by the user. Yet over time, the significant weight of the heavy, 20-ounce counterweights will cause the cams to move from their intended position, thereby making repeated sharpening of knives with the same cutting edge angle impossible without further precise adjustment of the position of the cams. Furthermore, the large number of parts mounted to the base member and the bolts and nuts used to mount them also produce environments for bacterial growth which makes it difficult to keep the device clean and sanitary.
A key advantage of this MOUSETRAP STEEL sharpener is that the criss-crossed sharpening steels act to sharpen both sides of the knife blade cutting edge simultaneously, so there is no need to swipe each side of the blade along a sharpening steel the same number of times to avoid blade damage. But, the criss-crossed sharpening steels act against the blade cutting edges in a manner that is approximate to the proper angle of the cutting edges, which may in some cases lead to suboptimal knife blade edge sharpening.
Moreover, the manual sharpening of knives can be time-consuming and require skill and diligence by the end user of the sharpening device. This can be a problem in particular for industrial operations like meat processing lines where large numbers of knives are used and dulled during the course of a day.
Thus, Razor Edge Systems has also commercialized a motorized “Heavy Duty System” knife blade sharpener that is used to manually restore a sharp cutting edge to a knife blade. It comprises a hollow grinder is used by the human operator to remove excess metal from the sides of the knife blade. By drawing the blade back and forth tip to handle between the two contra-rotating grinding wheels, the hollow grinder thins out the blade. Next, the knife is clamped by the operator into a D-ring clamping device that will provide the angle and control needed for further sharpening of the knife blade. The Edger features a rotating coarse sharpening wheel and a rotating fine sharpening wheel that are used by the operator sequentially to produce or restore the cutting edge back onto the knife blade. The coarse sharpening wheel on the Edger is used first to prepare the edge creating the correct angle. The fine sharpening wheel is then used to remove the burr created by the coarse wheel, thereby creating a sharp edge. Finally, a rotating buffer wheel removes any remaining pieces of metal from the knife blade, and smoothes the edge to remove any furrows (grooves) left behind by the Edger wheels. While the D-ring clamp facilitates the operator's manipulation of the knife blade across the Edger and buffer wheels, this is still a manually-operated procedure that requires the operator to follow the set procedure in order to produce a sharp edge. This includes proper orientation of the knife blade inside the D-ring clamp, proper alignment of the D-ring clamp with respect to the Edger and buffer wheels, and uncoupling of the D-ring clamp from the Heavy Duty System to flip the knife blade over 180 degrees during and between each of the coarse sharpening, fine sharpening, and buffing operations, which takes time and can lead to misalignment of the knife blade with respect to the rotating wheels. If improperly carried out, this Heavy Duty System will not properly sharpen the cutting edges of the knife's blade.
It is therefore easy to damage the cutting edge of the knife blade further if the sharpening exercise is performed poorly. Thus, most knife users need to send out their dulled knives to a professional sharpening service, or to replace the knife with a new knife. This can be time-consuming and expensive.
While electric knife sharpeners are available in the market, they can damage the knife blade edges if improperly used. Thus, efforts have been made to automate the knife sharpening process. But, it is not easy to replicate by a machine a process that inherently relies upon human judgment.
Robotic arms are known within the manufacturing industry. For example, U.S. Pat. No. 8,277,282 issued to Tanaka discloses an ultrasonic trimming apparatus designed to cut flexible material. An ultrasonic oscillator is supported by the end portion of an articulated robot arm with a cutter blade supported in turn by the ultrasonic oscillator. The cutter blade is ultrasonically vibrated by the ultrasonic oscillator to trim the material in accordance with a pre-stored pattern.
U.S. Pat. No. 6,224,459 issued to Stocker et al. describes a workplace inspection and handling system. A three-axis robotic system picks up a disk-shaped wafer like a semiconductor chip from an inspection station and places it at a second station for edge grinding of the chip. Multiple sliding members operating in different orthogonal directions are responsible for moving the robotic arm along the x-y-z axes. See also U.S. Pat. No. 6,881,130 issued to Stocker.
Robotic systems have also been applied within the industry to the sharpening of knife blades. For instance, U.S. Pat. No. 6,663,465 issued to Gross illustrates a grinding machine for sharpening (honing) knife blades. The sharpening station comprises a conventional arrangement of two contra-rotating grinding wheels operated by an electric drive motor. A robot having a manipulator and pneumatic gripper movable in six possible translatory and rotational degrees of spatial freedom picks up and moves the knife blade with respect to the grinding station. The knife blade is then drawn by the manipulator and gripper through the contra-rotating grinding wheels applying a constant force on the blade throughout the sharpening operation. The blade edge is ground in accordance with a pre-loaded data set represented by machine-independent neutral data that defines the blade in its three dimensions. The knife is then removed from the blade grinding machine and mounted within a measuring system that uses mechanical probes operated by a CNC-controlled system to sample the sharpened blade for its actual three-dimensional shape. By comparing the actual data set for the sharpened blade shape against the pre-loaded data set for the ideal blade shape, any difference determines whether the knife needs to be returned to the grinding station for further sharpening to produce a blade edge meeting the shape specifications for the knife.
U.S. Pat. No. 9,079,284 issued to Christenson et al. discloses an automated knife sharpening and cleaning system in which a gripper operated in three dimensions by three different axial drive assemblies picks up the knife and moves to the grinding station. The profile of the knife is sensed by sensors so that the grinding station can be adjusted according to the feedback provided by the sensors regarding the profile of the knife, and the position of the knife adjusted within the three-dimensional space. Once the knife blade is properly sharpened by the grinding assembly, the gripper assembly removes the knife and returns it to a storage tote.
U.S. Pat. No. 5,793,493 issued to Lane describes a system for estimating the cutting condition of a double-ground knife blade using a light, camera, and mirror to detect and compare the opposite cutting edges of the knife blade. The mirror allows the upper and lower blade bevel imager to be detected simultaneously by the camera.
U.S. Pat. No. 8,915,766 issued to Kolchin discloses another automated sharpening system in which the knife is manually placed in a holder with the cutting edge of the blade exposed. A sensor is configured to detect any burrs existing along the edge of the knife blade. An abrader set at the proper angle with respect to the knife blade edge then is moved along the blade edge to sharpen only those portions of the blade where the burrs exist.
U.S. Pat. No. 8,758,084 issued to Knecht et al. describes an apparatus for grinding hand knives comprising a CNC-operated gripper mechanism and a series of rotating, grinding, deburring, and polishing wheels. The knife is picked up by the gripper mechanism. A sensor measures the contour of the knife blade cutting edge which is then compared against stored data for the ideal profile for that knife blade. The gripper mechanism then moves the knife blade so that only those portions of the blade edge exhibiting imperfections are passed along the rotating, grinding, deburring, and polishing wheels for sharpening.
U.S. Published Application 2017/0087690 filed by Vogel et al. discloses an automated system for conditioning knife blades. A gripper assembly for the knife comprises one or more clamp arms for moving along x, y, and z axes, and rotatable in the roll direction, pitch direction, and yaw direction. A first measuring device constituting two lasers emits laser light beams for measuring the width and thickness of the knife blade along its length. The resulting data points are stored. A second measuring device constituting a light and a lens assembly then obtains images of the knife blade to measure the same thickness and width. These data points are then combined with the first set of data points to create a current edge profile for the knife blade. This current edge profile is then modified to obtain a modified edge profile. The gripper assembly manipulates the knife blade with respect to rotating grinder, buffer, and polishing wheels to sharpen the knife blade edge and restore it to its ideal state.
However, all of these prior art systems are very complicated in their structure and moving parts. It would therefore be beneficial to provide an automated hand tool sharpening and cleaning system that uses a robotic arm instead of a conventional CNC manipulation system in combination with a camera and associated software that creates an image of the blade or other working surface of the hand tool to profile it with the resulting data used to create machine control commands for the robotic arm to properly manipulate the hand tool blade or working surface with respect to a series of rotating, grinding, sharpening, and polishing wheels to appropriately sharpen its edge substantially along its entire length. The robotic arm can also be used to properly manipulate the sharpened blade or working surface inside a wash station to remove bits of metal and other residue resulting from the sharpening operation, and clean, scrub, and sanitize the hand tool for use in a domestic, industrial, sport, or hobby operation.